Studies are underway to determine the mechanism by which the assymetric distribution of saturated and unsaturated fatty acids in membrane phospholipids is affected. In the coming year we intend to examine the substrate and positional specificity of the glycerolphosphate acyltransferases in a variety of transplantable tumors and to determine the positional distribution of fatty acids in the phosphatidylcholine fractions derived from these tissues. Correlations will be sought between selective and nonselective positioning of fatty acids and the substrate and positional selectivity of microsomal and mitochondrial glycerol-3-P acyltransferases. It is anticipated that this work will complement our previous studies which indicate that the mitochondrial acyltransferase contributes to the selective placement of fatty acids in membrane phosphoglycerides.